There’s lots of money behind all that messaging. Just how much cash have Senate hopefuls in Georgia, Arkansas and Kentucky shelled out? (Pamela Kirkland/The Washington Post)

Get excited, because voters are casting ballots in six states holding high-stakes primaries. It's the busiest primary day of the year so far -- and the most consequential.

From tea party vs. establishment infighting in the West to a Democratic sprint to the left in the Northeast, there's a lot going on. But fear not! Here's where we come in. Below we give you the eight most important things to watch:

In the wildly unpredictable and increasingly nasty Georgia Senate race, there's only been one certainty the past few months: There will be a GOP runoff on July 22. Businessman David Perdue looks like a good bet to make the runoff, as his outsider message is hitting home thanks to the heaps of cash he has spent on advertising. Chamber of Commerce-backed Rep. Jack Kingston and Sarah Palin-backed former secretary of state Karen Handel are competing for a second spot, recent polls show. (A lot of undecided votes are still up for grabs.) The good news for Republican chances is that Reps. Paul Broun and Phil Gingrey, far right candidates with a knack for stoking controversy, appear to be out of the running. The winner is likely to take on highly touted Democratic recruit Michelle Nunn, a first-time candidate.

The only question about the Republican primary for U.S. Senate in Kentucky is the margin of minority leader Mitch McConnell's victory. Recent polls show him up by between 20 and 30 points. When Louisville businessman Matt Bevin launched his bid to unseat the Senate's top Republican, we thought McConnell might be in for an epic primary. McConnell is not popular and Bevin's personal fortune made him a candidate to watch. But the race has been anything but epic as the combination of missteps from the Bevin camp (um, cockfighting?) and a barrage of spending from McConnell and his allies prevented Bevin from ever posing a serious threat. That doesn't mean the final tally won't matter. As veteran observer Al Cross writes, Bevin could top 40 percent. McConnell will need every vote he can get in the fall against Secretary of State Alison Lundergan Grimes (D). If more than 40 percent of the GOP primary electorate is against him now, who's to say how many of them will come out for McConnell in November? Plus, there's the symbolic element. McConnell wants to be in a position of strength Wednesday on day one of the general election.

Polls close at 6 p.m. Eastern and Central.

3. Will Democrat Tom Wolf advance to a showdown against the nation's most vulnerable governor?

Tom Wolf (AP Photo/Keith Srakocic)

Polls show businessman Tom Wolf with a wide lead over the competition in the Democratic primary for governor in Pennsylvania. Thanks to his heavy ad spending, the technocrat Wolf has jumped to the top of the heap in a race that once looked potentially ripe for Rep. Allyson Schwartz to seize. But Schwartz's former ties to centrist groups and have gotten her into some trouble, as has the crowded field. She has been touting her support for Obamacare down the stretch, an approach that has stood out in an election cycle where the law has been politically toxic in so many other aces. Like Georgia, undecided voters could decide this one. But for Wolf to be upset, undecideds would have to break heavily toward one of his opponents. That doesn't seem likely to happen.

Polls close at 8 p.m. Eastern.

4. It's business versus tea party in Idaho. Business is poised for victory.

The anti-tax Club for Growth's first ever crowdsourced candidate is attorney Bryan Smith, who is challenging Rep. Mike Simpson (R-Idaho). But the business-backed Smith has gotten far more help from third-party groups overall. His backers -- most notably the Chamber -- have spent some $2.4 million on his behalf, compared to Smith's allies spending just $600,000. The Club has been off the air since last month, a sign this race isn't very competitive. If Simpson wins, it's another victory for the business wing of the tea party, which has shown a willingness to spend big in primaries this cycle. It would also be a let down for the Club, given how much excitement it generated about Smith.

Polls close at 10 p.m. Eastern.

5. Will Monica Wehby hold on in Oregon after a story about "stalking" her ex-boyfriend last year?

Last Thursday, pediatric neurosurgeon Monica Wehby seemed poised for victory in Oregon's GOP primary for U.S. Senate, despite a late barrage of outside spending from antiabortion groups hitting her from the right. But then came a Politico story Friday about a 2013 police report in which Wehby was accused by her ex-boyfriend of "stalking" him and entering his home without permission. Audio of the 911 call has also become public. Wehby was never arrested, but the distracting story threatens to veer her off-message for a while as the media continues to ask about it. Oregon votes by mail, and many primary ballots were cast in advance of Friday, suggesting Wehby will probably survive the primary and advance to a showdown against Sen. Jeff Merkley (D). Still, this is not the entry she envisioned.

Polls close at 11 p.m. Eastern.

6. Will a Clinton-backed U.S. House candidate advance in Pennsylvania?

In this Jan. 5, 1993 file photo, then-House Speaker Thomas Foley administers the House oath, during a re-enactment, to Rep Marjorie Margolies-Mezvinsky D-Pa. She is accompanied by husband Edward, left, and family, on Capitol Hill in Washington. (AP Photo/Dennis Cook)

Democrat Marjorie Margolies (then Margolies-Mezvinsky) lost her seat in Congress in the 1994 midterms in large part because of her vote for President Bill Clinton's economic plan. Twenty years later, she's back for a run at the House in a contested Democratic primary in Schwartz's district. Margolies has gotten fundraising help from Bill and Hillary Clinton. The former president even cut an ad for her. Margolies is the mother-in-law of Chelsea Clinton.

Polls close at 8 p.m. Eastern.

7. There are two GOP primaries for U.S. House in Arkansas worth following.

Republican Rep. Tom Cotton (R-Ark.), above, is vacating his 4th district seat to run for U.S. Senate. (AP Photo/Danny Johnston)

Democrats are bullish about competing in the open 2nd and 4th congressional districts, where they've recruited capable candidates and the Republican fields are less settled. The 2nd district is Democrats' better bet. The GOP nominee there -- probably either state Rep. Ann Clemmer or banker French Hill -- will face former North Little Rock Mayor Patrick Henry Hays (D) in the fall. In the 4th district, where incumbent Rep. Tom Cotton (R) is leaving his seat to run for the U.S. Senate, the Republican frontrunner is state House Majority Leader Bruce Westerman. The GOP nominee will face former FEMA chief James Lee Witt (D).

Polls close at 8:30 p.m. Eastern.

8. Which Republican will take on the last white Democrat from the Deep South in the House?

Rep. John Barrow (D-Ga.) in 2012. (John Bazemore/Associated Press)

Five Republicans are vying for a chance to take on Rep. John Barrow of Georgia, the last white Democrat from the Deep South in the U.S. House. Barrow survived against the odds last election cycle and his reward is that once again Republicans are eagerly eyeing a chance to unseat him. But first, they have to sort out who their nominee will be. The race may be headed to a July runoff, which would be good news for Barrow. The GOP frontrunner is construction company Rick Allen, who lost in the 2012 primary.

Polls close at 7 p.m. Eastern.

Updated at 8:53 a.m. on 5/20

Sean Sullivan has covered national politics for The Washington Post since 2012.

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